remove unused Linux 2.0 compat code, otherwise c6x without NPTL is broken

libc/stdlib/system.c

@@ -20,11 +20,7 @@
 
 extern __typeof(system) __libc_system;
 #if !defined __UCLIBC_HAS_THREADS_NATIVE__
-/* uClinux-2.0 has vfork, but Linux 2.0 doesn't */
 #include <sys/syscall.h>
-#ifndef __NR_vfork
-# define vfork fork
-#endif
 
 int __libc_system(const char *command)
 {